Particular matter suspended in a gas is encountered in many industries. In some industries, such particulate matter is a valuable product, for example, starch, that is to be recovered. For others, such as the metal working industry, the particulate matter may be simply dust to be removed from the air. Systems for cleaning an air or gas stream laden with particulate matter include air filter assemblies that have filter elements disposed in a housing. The filter element may be a bag or sock of a suitable fabric or pleated paper. Cleaning is accomplished by periodically pulsing a brief jet of pressurized air into the interior of the filter element to reverse the air flow through the filter element. Such air filter assemblies are disclosed in, for example, U.S. Pat. No. 4,218,227 (Frey) and U.S. Pat. No. 4,395,269 (Schuler), which patents are hereby incorporated by reference.
Venturi elements are sometimes used to direct the jet of pressurized air into the filter element and to recover pressure energy as air exits the filter element. Often, the inlet end of the Venturi element is either outside the filtering chamber or extends into the interior of the filter element. For example, U.S. Pat. No. 4,218,227 (Frey) discloses mounting a Venturi with the inlet of the Venturi element resting on the side of the partition of the filter chamber opposite the filter element. U.S. Pat. No. 3,942,962 (Duyckinck) discloses a Venturi element with the Venturi inlet portion extending into the interior of the filter element.
In a standard design of Venturi systems for application with pulse-jet-cleaning, a high pressure drop (or pressure differential) occurs across the Venturi element. Pulse-jet cleaning systems generate loud noise as the back-pulse valves open and close to deliver the highly pressurized air necessary to overcome the pressure in the filter element for reversing the flow of air therein. U.S. Pat. No. 5,562,746 to Raether describes, among other things, an air-filtration system that results in reduced noise level and lower energy loss during the filtration of particulate matter-laden air and pulse-jet cleaning of the filter elements. U.S. Pat. No. 5,562,746 is hereby incorporated by reference.